This invention relates to self-drilling bolts.
The extremely rapid expansion experienced in the civil engineering sector, in particular in the construction field, and also the continuous improvement in construction techniques have given rise to the need for efficient processes which will enable anchoring bolts and pins, particularly those of large diameter, to be fixed rapidly and economically in hard walls, for example of reinforced concrete.
However, the processes employed at the present time are not at all satisfactory for this need. In fact, a whole series of operations has to be carried out in order to anchor a securing bolt by the traditional methods, namely: drilling a hole by, in general, mechanical means; clearing out the hole; sinking the securing bolt and finally plugging this bolt by appropriate means.
It has been proposed to provide the bolt itself with drilling teeth so that, when fixed to the end of a tool, it itself mechanically drills the hole in which it is to be subsequently anchored. These operations are not made easier however since it is also necessary to remove the bolt after the drilling so that the hole can be cleared out before inserting appropriate means which will ensure the subsequent anchoring of the bolt. Furthermore, such a process is relatively expensive and does not remove all the defects inherent in all the mechanical drilling methods, concerning the geometry of the tool employed as well as the difficulty in drilling composite materials.
In fact, working with composite materials by mechanical means poses special problems connected with the different characteristics of the elements comprising these materials. For example, the mechanical drilling of reinforced concrete by steel drilling bits means, in principle, changing from one type of tool to another depending on whether, at any given time during the drilling, concrete or steel is being drilled. In practice such a procedure is clearly not practicable, both on account of loss of time and the danger of damaging the tool heads.
A process for anchoring bolts in a refractory material has also been proposed, consisting in utilising the vibrational energy produced by a mechanical vibrator to effect the drilling by the bolt itself, the said bolt then being plugged in the drilled hole by means of a special alloy which first melts on account of the heat generated by friction and then cools around the bolt. Such a process is however relatively complex to put into operation and it remains strictly limited to the drilling of refractory materials, to the exclusion of composite materials.
Finally, bolt anchoring processes using explosives are known. These processes are however restricted to anchoring small diameter bolts, in general less than 8 mm in diameter.